This invention relates to an improved high pressure nozzle with on-off capability. The invention is herein described by reference to preferred embodiments thereof; however, it will be recognized that certain modifications and changes may be made therein with respect to details without departing from the essential features of the invention.
A valve is required in jet cutting systems for controlling the discharge of the water jet and flow of the fluid which may have a pressure as high as 60,000 psi or more. In conventional apparatus the valve is installed in the supply tube upstream of the cutting nozzle. Each time the valve opens or closes the supply tube between the valve and jet forming element is subjected to a pressure change equal to the maximum operating pressure.
In conventional apparatus, when the valve is rapidly opened, a compression wave is formed that propagates toward the jet forming element. Simultaneously with the formation of the pressure waves an expansion wave is formed at the valve which propagates toward the source of the high pressure. The waves thus formed upon the opening of the valve reflect off various portions of the apparatus, causing fluctuating pressures in the supply tubes. If the fatigue resistance of the supply tube is not sufficient to withstand the fluctuating pressure, rupture of the tube and danger to the operator may result. In cutting apparatus the supply tubes are, therefore, normally made of substantial thickness and strength to withstand the pressure fluctuations. Even with such thick wall supply tubes there is a possibility of metal fatigue caused by repeated passage of the waves generated by valve operation. The pressure waves generated are especially severe when a large chamber is positioned immediately upstream of the jet-forming element as is often the case when a high quality cutting jet is required.
Current liquid jet cutting apparatus systems commonly use a synthetic saphire jewel with an axial orifice as the jet-forming element to promote long life under the high jet speeds used. The jewel is normally mounted in the nozzle by an elastomeric washer to provide a resilient mounting. With conventional valving systems the alternate pressurization and depressurization of the system and resultant pressure waves may cause the jewel jet-forming element to become dislocated or dislodged from its mounting. When the jewel jet-forming element is dislocated or dislodged, disassembly of the apparatus is required to reinsert the jewel.
One approach to pressure wave associated fatigue has been to insert a hydraulic accumulator in the tube supplying the valve. The accumulator reduces the magnitude of the pressure waves passing through the supply tubing upstream of the valve, but is of little or no help for the tubing downstream of the valve. The insertion of an accumulator adds to the expense and weight of the system, however, and cannot be used in all situations. Accordingly, a need has arisen for an alternative means for preventing generation of pressure waves due to valve opening and closing.